Saute tuna in oil for 2 minutes per side. Add wine and tomatoes. Simmer for 10 minutes. Season with salt and remove from heat. Using a bit more olive oil, saute onion in another pan for 5 minutes. Add potatoes, and both peppers. Saute for 15 minutes. Place tuna on plate, cover with tomato sauce and sprinkle with the sauteed vegetables. Serve.